Token ring road traffic control and congestion management

Read an article the other day in Wired, A system to cut traffic that just might work, about two MIT students doing research to help Singapore better manage traffic congestion. They have come up with a sort of token ring network for traffic.

In their approach every car when it enters a “congestion zone” is suppplied an electronic token and when that car leaves the zone it retires it’s token (sound familiar). When the zone is too congested, no new tokens are handed out and cars are re-routed around the zone using GPS provided directions.

It seems a bit hokey but using tokens to control congestion is an old technology and works just fine. The problem with applying tokens to controlling road congestion is that it’s not so easy to re-route someone around a zone if you have to go into it for work or entertainment.

Traffic congestion management today

Most congestion management schemes use congestion toll pricing with transponder and radio transmitters/receivers at entry points into congestion zones. In this fashion metropolitan areas can raise and lower toll pricing on traffic that enters the zone as an incentive to reduce traffic. But this requires special purpose transponders in every car and radio towers at every entry and exit point which fixes the congestion zone boundaries and has a high initial fixed costs.

Singapore’s congestion approach is similar with transponders and radio readers at select entry and exit point locations around the city.

Traffic management via tokens

What the MIT researchers have done is to use a broader WiFi type of radio transmitter in their car transponders with a wider range and use cell tower-like receivers around a metro area to triangulate where a car is and when it’s in a congestion zone and to transfer this information to a central repository.

One advantage to the MIT solution is that the congestion zones are no longer fixed, but can become whatever boundary a city administrator wants to create on a map of the city. This way, different zones could be attempted as experiments whenever it made sense to do so.  Sort of like having a completely configurable congestion zone which can be turned on and off based on the requirements of the moment. And the zones don’t even have to be a polygon at all, any closed form, that could be drawn on a map could represent a new zone.   And of course you could have multiple layers of zones. All this could be almost instantly configurable and trial-able on a whim, like a software defined traffic management (SDTM).

I suppose one problem with using SDTM for toll pricing is that people would need to know ahead of time the cost of traveling through a zone. Maybe that’s why the token approach is better because without a token, you are directed to stop or on another route, outside or around the zone. In one waye tokens could be used as sort of a sophisticated onramp stop signal, that only allows passage when a token frees up.

Maybe token’s should be retired not just when you leave a zone but when you stop moving  or when the engine is turned off as well, that way as cars are parked, their tokens could be freed up for other cars.

How you get people to go along with the token management is another question. As the system is tracking cars automatically, one could automatically fine drivers for violating the token scheme.


Thank goodness my commute days are long gone.  I get the feeling it’s going to become a lot more interesting driving to work in the future.


Photo Credits: World Class Traffic Jam by JosieShowaa